The supply of electricity to domestic premises cannot always be guaranteed, and can fail due to a variety of external conditions. Domestic heating appliances generally require an electrical power supply, even where gas is the primary fuel, to power control circuitry, igniters, etc. A mains power failure therefore leaves the dwelling without its main source of heat, as well as lighting, etc. In the event of such a failure a great deal of discomfort is generally suffered by the consumer, and where the remote, very old or very young are concerned this can be a far more serious matter.
Arrangements for a back-up generating facility for domestic premises generally consist of engine-driven generators that need to be connected into the isolated circuit after the failure has occurred. These then provide power to the domestic circuit until the network supply is restored. The generator then needs to be turned off, disconnected and the mains supply reconnected. This arrangement provides back-up power but has disadvantages in generator storage and/or movement into position when required, alternative fuel storage for the generator, regular maintenance to ensure reliability, and the need for safe switching. Such a facility cannot be employed in an urban dwelling where no space, such as a garage, is available to house the generator.
Domestic heating systems that incorporate an internal power supply have been developed, such as in DE 29706869, where a back-up storage battery can provide power to the heating system for a limited time. A prolonged power cut would still however result in a loss of heat.
Domestic photo-voltaic systems exist that can provide a back-up electrical supply, but these are dependent on weather conditions and require daylight to generate. Wind-power too depends on external conditions, and cannot be relied upon for emergency power. Fuel cells could provide a potential back-up power supply, as in JP 4308432, where solar or fuel cells are used to provide back-up power, but only feed a DC system. The back-up is external to any piece of equipment and not specific to a heating system.
Recently, the present assignee has proposed a domestic combined heat and power (dchp) unit comprising a linear free piston) Stirling engine (LFPSE). In “Microgen—Cogeneration for the home”, by Dann et al, at the International Gas Research Conference, San Diego, 1998, a review of the perceived requirements of a microcogeneration system and an introduction to the principles underlying the Stirling engine dchp is provided. As this paper indicates, the provision of standby power when power cuts occur is a desirable feature of such a dchp. The paper also indicates, without detailed explanation, that such provision presents implications.
The present invention is concerned in particular, but not exclusively, with addressing the implications of providing standby power from a dchp.